DDWiki/实践/后端/C#基础/19.C#中关于时间.md

>关于年的问题
- DownList显示年，可根据当前的年份，具体代码
  ```
   public List<string> GetYears()
        {
            List<string> allYears = new List<string>();
            var now = DateTime.Now;
            int currentYear = now.Year;//2019
            allYears.Add((currentYear - 3).ToString());//2016
            allYears.Add((currentYear - 2).ToString());//2017
            allYears.Add((currentYear - 1).ToString());//2018
            allYears.Add(currentYear.ToString());//2019
            allYears.Add((currentYear + 1).ToString());//2020
            allYears.Add((currentYear + 2).ToString());//2021
            allYears.Add((currentYear + 3).ToString());//2022
            return allYears;
        }
  ```

> 关于月的问题
- DownList显示月。因为月是具体的24个月，可直接增添值
```
 public List<string> GetMonths()
        {
            List<string> allMonths = new List<string>();
            allMonths.AddRange(new List<string> { "01","02","03","04","05","06","07","08","09","10","11","12"});
            return allMonths;
        }
```

> 关于天的问题
- 因为每年的每个月的天数不确定，可以根据请求或者选择的年月进行显示天数
```
/// <summary>
        /// 获取天
        /// </summary>
        /// <param name="year"></param>
        /// <param name="month"></param>
        /// <returns></returns>
        public List<string> GetDays(string year, string month)
        {
            var result = new List<string>();

            if(!string.IsNullOrEmpty(year) && !string.IsNullOrEmpty(month))
            {
                //拼接月和年 2019-04
                string yearAndMonthStr = year + "-" + month;
                //月初 2019-04-01
                DateTime beginTime = DateTime.Parse(yearAndMonthStr + "-01");
                DateTime endTime = DateTime.Parse(beginTime.AddMonths(1).AddDays(-1).ToShortDateString());
                //月末
                for (DateTime dt = beginTime; dt <= endTime; dt = dt.AddDays(1))
                {
                    result.Add(dt.Day.ToString());
                }
            }
            
            return result;
        }
```
> 时间格式转换（12或者24小时）
```
string time = Convert.ToDateTime(date).ToString("yyyy-MM-dd HH:mm");//HH为24小时
string time = Convert.ToDateTime(date).ToString("yyyy-MM-dd hh:mm");//hh为12小时

```